Short Chain Branching Research Articles

GPC-VIS-MALS study of EVA copolymers: Quantification and interactions of SCB and LCB

Long-chain branching (LCB) is a structural phenomenon that affects important properties in polyethylene (PE) and some copolymers. Quantification of LCB frequency (λ) can be carried out by gel permeation chromatography dotted with detector for viscosity (GPC-VIS) or light scattering (GPC-MALS) by calculating branching indexes against a linear reference. In copolymers, interactions between LCB and SCB (short chain branching) have been described and lead to errors in quantification.In this work, ethyl vinyl acetate (EVA) copolymers of composition ranging 3–20 wt% VA have been studied. A numerical method, developed for the reduction of GPC-VIS and GPC-MALS data of PE, was used for quantifying molecular weights, intrinsic viscosities and gyration radius, as well as the confident ranges. Reliable results were obtained despite the low LCB determined values.A low density polyethylene was also included and compared. Discrepancies in the scaling laws for gyration radius and intrinsic viscosity reveal a strong effect of SCB which was confirmed by the structure factor and its dependence on molecular weight and comonomer content. However, the recently designed gpcBR index revealed to be nearly independent on the short chain branching and allowed detecting differences between apparently similar samples.

Molecular structure and enzymatic hydrolysis properties of starches from high-amylose maize inbred lines and their hybrids

High-amylose maize starch has health benefits and special industrial uses. In this study, starches were isolated from normal maize and high-amylose inbred and hybrid maizes. Their molecular structure and enzymatic hydrolysis properties were investigated and analyzed. The high-amylose hybrid maize starch contained lower amylose, intermediate component, amylopectin long branch-chains, and amylopectin average chain length, and higher amylopectin short branch-chains than did high-amylose inbred maize starch. High-amylose maize starch was more resistant to α-amylase and amyloglucocidase hydrolysis and had a significantly lower hydrolysis rate coefficient than normal maize starch did. The native, gelatinized and retrograded starches of the high-amylose hybrid maize had significantly higher rapidly digestible starch and lower resistant starch than those of the high-amylose inbred maize. The retrogradation of gelatinized starch markedly increased the resistance of high-amylose starch to in vitro digestion. The high contents of amylose and intermediate component and the long branch-chains of amylopectin increased the resistance of maize starch to enzymatic hydrolysis and in vitro digestion.

Communication: Role of short chain branching in polymer structure and dynamics.

A comprehensive understanding of chain-branching effects, essential for establishing general knowledge of the structure-property-phenomenon relationship in polymer science, has not yet been found, due to a critical lack of knowledge on the role of short-chain branches, the effects of which have mostly been neglected in favor of the standard entropic-based concepts of long polymers. Here, we show a significant effect of short-chain branching on the structural and dynamical properties of polymeric materials, and reveal the molecular origins behind the fundamental role of short branches, via atomistic nonequilibrium molecular dynamics and mesoscopic Brownian dynamics by systematically varying the strength of the mobility of short branches. We demonstrate that the fast random Brownian kinetics inherent to short branches plays a key role in governing the overall structure and dynamics of polymers, leading to a compact molecular structure and, under external fields, to a lesser degree of structural deformation of polymer, to a reduced shear-thinning behavior, and to a smaller elastic stress, compared with their linear analogues. Their fast dynamical nature being unaffected by practical flow fields owing to their very short characteristic time scale, short branches would substantially influence (i.e., facilitate) the overall relaxation behavior of polymeric materials under various flowing conditions.

Synthesis and Thermal Characterization of Precision Poly(p‐cyclohexylene alkylene)s via Acyclic Diene Metathesis Polycondensation

The synthesis and thermal characterization of poly(p‐cyclohexylene alkylene)s (PPCs) is described. Polymers containing 1,4‐cyclohexylene units on every 15th, 19th, and 21st chain carbon are prepared by the acyclic diene metathesis polycondensation of symmetric α,ω‐dienes obtained from the α‐alkylation of cyclohexane‐1,4‐dicarbonitrile. Exhaustive hydrogenation of the unsaturated polymers yields fully cycloaliphatic polymers with excellent resistance to thermal degradation. The thermal analysis of the unsaturated and saturated materials reveals a strong influence of the cis‐alkene and cis‐1,4‐cyclohexylene on the final thermal properties of each material. PPC exhibits higher melting temperature and thermal stability than similar materials, in which the aliphatic ring is replaced by aromatic rings or short chain branches. The melting behavior is discussed in terms of the higher flexibility and enhanced intermolecular packing of the symmetrical 1,4‐cyclohexylene units incorporated within the chain. image

Influence of molecular architecture on the entanglement network: topological analysis of linear, long- and short-chain branched polyethylene melts via Monte Carlo simulations.

We present detailed results on the effect of chain branching on the topological properties of entangled polymer melts via an advanced connectivity-altering Monte Carlo (MC) algorithm. Eleven representative model linear, short-chain branched (SCB), and long-chain branched (LCB) polyethylene (PE) melts were employed, based on the total chain length and/or the longest linear chain dimension. Directly analyzing the entanglement [or the primitive path (PP)] network of the system via the Z-code, we quantified several important topological measures: (a) the PP contour length Lpp, (b) the number of entanglements Zes per chain, (c) the end-to-end length of an entanglement strand des, (d) the number of carbon atoms per entanglement strand Nes, and (e) the probability distribution for each of these quantities. The results show that the SCB polymer melts have significantly more compact overall chain conformations compared to the linear polymers, exhibiting, relative to the corresponding linear analogues, (a) ∼20% smaller values of 〈Lpp〉 (the statistical average of Lpp), (b) ∼30% smaller values of 〈Zes〉, (c) ∼20% larger values of 〈des〉, and (d) ∼50% larger values of 〈Nes〉. In contrast, despite the intrinsically smaller overall chain dimensions than those of the linear analogues, the LCB (H-shaped and A3AA3 multiarm) PE melts exhibit relatively (a) 7-8% larger values of 〈Lpp〉, (b) 6-11% larger values of 〈Zes〉 for the H-shaped melt and ∼2% smaller values of 〈Zes〉 for the A3AA3 multiarm, (c) 2-5% smaller values of 〈des〉, and (d) 7-11% smaller values of 〈Nes〉. Several interesting features were also found in the results of the probability distribution functions P for each topological measure.

A new insight into the conformation and melt dynamics of hydrogenated polybutadiene as revealed by computer simulations.

Extensive molecular dynamics simulations of the macromolecular conformation and the melt dynamics for model polymers of different molecular weights have been carried out. The selected models are hydrogenated polybutadienes with a 2% content of ethyl branches and linear polyethylene. It will be shown that the density and chain stiffness are clearly affected by both the molecular weight and the presence of ethyl branches. Furthermore, the results obtained from the simulations on the molecular size and, more remarkably, chain dynamics, perfectly match the neutron scattering experiments performed by Zamponi et al. in hydrogenated polybutadienes. We observe a clear chain contraction and a slow dynamics for the hydrogenated polybutadiene with respect to the linear chain of the same molecular length. Using the Likhtman-McLeish definitions, the obtained values of the entanglement relaxation time (τe) and the tube diameter (a) are found to be in agreement with the available experimental data (by rheology and neutron spin echo) as well as with those obtained by the simulations. Finally, a very good agreement of diffusion coefficients as a function of the molecular weight between simulations and experiments is observed. Therefore, there exists a clear difference between the results obtained for branched and linear polyethylene, accounting for a definitive effect of the short chain branching on the conformational properties and the melt dynamics of polyolefins.

Reprint of: Effect of Mo-modification over Phillips CrOx/SiO2 catalyst for ethylene polymerization

Phillips CrOx/SiO2 catalyst is an important catalyst for industrial production of polyethylene. In this work, a Mo-modified Phillips catalyst for ethylene polymerization (defined as CrMo/Si) was developed. The characterizations of the Phillips catalyst (defined as Cr/Si) and the CrMo/Si catalyst by temperature programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS) showed an obvious interaction between the chromium and molybdenum components on the silica support. The ethylene polymerization performances at different conditions, in terms of H2 responds, polymerization temperatures, and the copolymerization with 1-hexene were systematically investigated. Although the polymerization activity of the CrMo/Si catalyst was lower, the copolymer presented a higher molecular weight (MW) and a broader molecular weight distribution (MWD). The Mo-modified Phillips catalyst (CrMo/Si) exhibited 67% higher 1-hexene incorporation ability as determined by 13C NMR. Moreover, the short chain branch distribution (SCBD) of the copolymer obtained via the CrMo/Si catalyst was also improved as confirmed by temperature rising elution fractionation (TREF) cross successive self-nucleation and annealing (SSA) methods. The results of TREF and SSA showed that the amount of short chain branches for the copolymer was increased in the high MW part, which would benefit for the long term mechanical property of polyethylene.

Structure and thermal properties of ethylene/4-methyl-1-pentene copolymers: Effect of comonomer and monomer sequence distribution

A series of ethylene/4-methyl-1-pentene (E/4M1P) copolymers is synthesized, using the Ti(IV) diisopropoxy complex bearing a dianionic [O−,S,O−] bis(phenolato) ligand, in combination with methylalumoxane, as catalyst system. The semicrystalline copolymers are characterized by NMR, DSC, WAXD and SAXS. The structure and the thermal behavior of the copolymers are strongly influenced by composition and monomer sequence distribution. The copolymer crystallinity decreases as a function of 4M1P content, while an increase of the periodicity due to the enhancement of the amorphous interlamellar thickness is registered. The non-homogeneous distribution of the 4M1P units along the polymer chains is evidenced by the multimodal crystallization and melting behavior. The chain heterogeneity of the copolymers is investigated by successive self-nucleation and annealing thermal fractionation evaluating the methylene sequence length, the short chain branching and the lamellar thickness. In order to get more information on the comonomer distribution in the copolymers, solvent extraction is performed and all the fractions are characterized by thermal and X-ray techniques.

The influence of short-chain branching on the morphology and structure of polyethylene single crystals

The influence of short-chain branching on the formation of single crystals at constant supercooling is systematically studied in a series of metallocene catalyzed high-molecular-weight polyethylene samples. A strong effect of short-chain branching on the morphology and structure of single crystals is reported. An increase of the axial ratio with short-chain branching content, together with a characteristic curvature of the (110) crystal faces are observed. To the best of our knowledge, this is the first time that this observation is reported in high-molecular-weight polyethylene. The curvature can be explained by a continuous increase in the step initiationstep propagation rates ratio with short-chain branching, that is, nucleation events are favored against stem propagation by the presence of chain defects. Micro-diffraction and WAXS results clearly indicate that all samples crystallize in the orthorhombic form. An increase of the unit cell parameter a(0) is detected, an effect that is more pronounced than in the case of single crystals with ethyl and propyl branches. The changes observed are compatible with an expanded lattice due to the presence of branches at the surface folding. A decrease in crystal thickness with branching content is observed as determined from shadow measurements by TEM. The results are in agreement with additional SAXS results performed in single crystal mats and with indirect calorimetry measurements. (c) 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 1751-1762

Studies on the Application of Filter‐Based IR Detector for Polyolefin Characterization with HT‐SEC

SummaryEven though polyolefins are simple polymers from a chemical structure point of view, their full characterization in practice is still an intriguing task. Basic macromolecular characteristics of polyethylene or polypropylene like molar mass moments and their distributions (MMD) but also chain conformation and thus information on long‐chain branching, can be addressed with high‐temperature size‐exclusion chromatography (HT‐SEC). Hyphenation of infrared detection to size‐exclusion chromatography expands possibilities of SEC even more and allows to reveal comonomer incorporation across molecular weight and thus generate a fingerprint of a given catalytic system used in polyolefin synthesis. Multiband filter‐based infrared detector gives an easy and fast access to so‐called short chain branching distribution (SCB) vs MMD by coupling to HT‐SEC. In this work, we summarize recent findings on application of a filter‐based IR detector (IR5‐MCT) towards characterization of polyolefins synthesized with different catalytic systems and varying comonomer types. It is found that for copolymers of polyethylene with 1‐butene, 1‐hexene or 1‐octene (non‐C3), one linear calibration line can be used in the range up to 70 CH3/1000TC, thus covering the range necessary for common applications like for instance HDPE or LLDPE. For ethylene‐propylene copolymers (C3), over the broad range up to 333 CH3/1000TC, the calibration line is best fitted to a second order polynomial. C3 copolymers show a different behavior compared to non‐C3 copolymers, irrespective the amount of comonomer incorporated in the polymer. We show that mixtures of PP and PE homopolymers result in equivalent response as the copolymers of the same average composition and thus can also be used to set up calibration lines. Based on this evaluation practical aspects of IR5‐MCT calibration are discussed.

Separation of bimodal high density polyethylene using multidimensional high temperature liquid chromatography

High-temperature two-dimensional liquid chromatography (HT 2D-LC) using HT-HPLC as first dimension and HT-SEC as second dimension holds enormous potential to investigate the distribution according to molar mass and chemical composition of bimodal high density polyethylene (BiHDPE), as it avoids drawbacks of crystallization-based techniques. In this study, we have stepwise optimized the chromatographic parameters of 1D, comprising gradient slope and temperature, using model homo- and copolymers of ethylene with the aim to minimize the impact of molar mass on the compositional separation. Then the HT-HPLC was hyphenated to HT-SEC and optimum conditions for the volume of the sample transfer loop were probed with regard to the resolution of BiHDPE into the individual constituents HDPE and LLDPE. A particular important aspect was the use of infrared (IR) detection, and the demands it puts on the chromatographic aspects: We have shown that IR detection can be successfully applied in HT 2D-LC of BiHDPE, which is broadly distributed with regard to short chain branching and molar mass, only when the separation in 2D is optimized with regard to chromatographic resolution. As final result a bimodality is evident in the contour and the 3D surface plots as well as in both HPLC and SEC projections generated from HT 2D-LC.

Introduction of chromium species into the (SiO2/MgO/MgCl2)·TiClx Ziegler–Natta catalyst for better catalytic performance

A novel chromium-modified (SiO2/MgO/MgCl2)·TiClx Ziegler–Natta ethylene polymerization catalyst with improved catalytic properties is successfully developed. The catalyst is prepared through co-impregnation of water-soluble magnesium and chromium compounds with SiO2 followed by calcination in dry air and refluxing reaction with TiCl4 to synthesize magnesium dichloride in situ, and the supporting of titanium species is also accomplished simultaneously. By characterization of the catalysts and the polymers, several key factors such as cocatalyst concentration, the addition amount of chromium species, the effect of hydrogen and 1-hexene in ethylene polymerization are systematically investigated. Compared with the original (SiO2/MgO/MgCl2)·TiClx Ziegler–Natta catalyst, the novel Cr-modified catalyst with proper initial addition amount of chromium shows better catalytic performance with 13% higher activity, 40% higher hydrogen response, and 20% higher 1-hexene incorporation ability with better short chain branch distribution.

Molecular chain heterogeneity of a branched polyethylene resin using cross-fractionation techniques

The typical standard long chain branching (LCB) polyethylene (PE) SRM1476 is issued by the American National Bureau of Standards, which is widely used as a standard reference material in chromatographic experiments. Although some works have been reported in literatures, they are not consistent, such as the data about its molecular weight and molecular weight distribution. Therefore, it is necessary to further investigate the microstructure features of SRM1476 in order to better serve as a reference object in comparison with other unknown resins. In this study, the molecular chain heterogeneity of SRM1476 is investigated extensively and compared with the linear PE SRM1475. Based on the characterization of the original sample, SRM1476 actually has both LCB and short chain branching (SCB) structures, as well as the SCB content is more than LCB content in 13C-NMR results. After successive self-nucleation and annealing (SSA) thermal fractionation, SRM1476 shows a broad-range endotherm with multiple melting peaks (more than eight peaks), which proves the molecular chain heterogeneity in SRM1476. SRM1476 is fractionated into nine fractions by preparative temperature rising elution fractionation (TREF). At the high elution temperature region, the amounts of fractions are more than 90 %, and their molecular weights are higher. At the low elution temperature region below 50 °C, molecular weights of fractions are lower and their amounts are less than 5 %. Differential scanning calorimetry (DSC) melting curves of TREF fractions with higher elution temperatures shift toward higher temperature with sharper melting peaks. In the results of TREF-SSA cross-fractionation, each fraction shows a broad-range endotherm with multiple melting peaks that shift toward the high elution temperature region with the elution temperature. The arithmetic mean methylene sequence lengths of TREF fractions gradually increase from 33 to 105 as elution temperature increases. Results from TREF-DSC and TREF-SSA cross-fractionations indicate that SRM1476 and its TREF fractions have both intramolecular and intermolecular heterogeneity.

Relationships between amylopectin molecular structures and functional properties of different-sized fractions of normal and high-amylose maize starches

The amylopectin molecular structures and functional properties of different-sized fractions of normal and high-amylose maize starches were investigated and compared in this study. The different-sized fractions of normal starch showed similar amylopectin molecular structures and functional properties. The small-sized fraction of high-amylose starch had significantly higher amylopectin long branch-chain and average branch-chain length than its counterpart medium- and large-sized fractions. The swelling power, gelatinization enthalpy, and hydrolysis and digestion degrees of high-amylose starch significantly decreased with decrease of granule size, and were significantly positively correlated with amylopectin short branch-chain and negatively correlated with amylopectin long branch-chain and average branch-chain length. The gelatinization peak temperature and resistant starch content increased with decrease of granule size, and were significantly positively correlated with amylopectin long branch-chain and average branch-chain length and negatively correlated with amylopectin short branch-chain. The hierarchical cluster analysis indicated that the large-sized fraction of high-amylose starch was significantly different from the medium- and small-sized fractions of high-amylose starch but more relative with normal starch. The above results could provide important information for the applications of different-sized fractions of high-amylose maize starch.

Simulation of semi-crystalline polyethylene: Effect of short-chain branching on tie chains and trapped entanglements

A Monte-Carlo simulation method for assessing the tie chain and trapped entanglement concentration in linear polyethylene was extended to enable the simulation of explicitly branched polyethylene. A subroutine was added to the model making possible the incorporation of different branch lengths and distributions. In addition, the microstructure of branched polyethylene was considered to be made of lamellar stacks of different thicknesses, acknowledging the segregation phenomenon during crystallization. Also, based on complete exclusion of bulky branches from the crystal lattice, a ‘pull-out’ mechanism was developed for the relaxation of branched parts of polyethylene chains in the vicinity of the crystal layer. Simulations of two series of real polyethylene samples showed the effect of short-chain branching on the concentrations of tie chains and trapped entanglements. Introducing a few branches to an unbranched polyethylene increased the concentration of inter-lamellar connections significantly. This effect decayed if the number of branches was further increased. The tracking of the position of all the carbon atoms during the crystallization process was implemented in the model, making the average square end-to-end distance <r2> of polyethylene chains calculable. Simulation of chains with the same molar mass but with different branch contents showed a reduction in the average end-to-end distance with increased branching. The use of real molar mass distribution data was also added to the model features.

Comparative structure of starches from high-amylose maize inbred lines and their hybrids

High-amylose maize starch is of interest because of its health benefits and industrial uses. Hybrid maize is widely grown for the practical and economical value of heterosis. However, starch structure of high-amylose hybrid maize has seldom been reported compared with that of high-amylose inbred maize. In this study, structure of starches from high-amylose maize inbred lines and their hybrids was investigated and compared. Starch granule became smaller in size and more spherical, oval or elongated in shape with increasing amylose content. Hybrid maize starch had lower amylose content and long branch-chain of amylopectin and higher short branch-chain and branching degree of amylopectin than inbred maize starch. Inbred maize starch had B-type crystalline structure with low relative crystallinity, but hybrid maize starch had CB-type crystalline structure and high relative crystallinity. Hybrid maize starch had lower degree of order at a short-range scale on the edge of starch granule than inbred maize starch. Hybrid maize starch had higher double helix content and lower amorphous starch than inbred maize starch. Hybrid maize starch had higher peak intensity and longer Bragg spacing of lamellar structure than inbred maize starch. Hybrid maize starch had lower gelatinization temperature and higher gelatinization enthalpy and swelling power than inbred maize starch. The different structural properties of starches had significant correlation.

Effect of Mo-modification over Phillips CrOx/SiO2 catalyst for ethylene polymerization

Phillips CrOx/SiO2 catalyst is an important catalyst for industrial production of polyethylene. In this work, a Mo-modified Phillips catalyst for ethylene polymerization (defined as CrMo/Si) was developed. The characterizations of the Phillips catalyst (defined as Cr/Si) and the CrMo/Si catalyst by temperature programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS) showed an obvious interaction between the chromium and molybdenum components on the silica support. The ethylene polymerization performances at different conditions, in terms of H2 responds, polymerization temperatures, and the copolymerization with 1-hexene were systematically investigated. Although the polymerization activity of the CrMo/Si catalyst was lower, the copolymer presented a higher molecular weight (MW) and a broader molecular weight distribution (MWD). The Mo-modified Phillips catalyst (CrMo/Si) exhibited 67% higher 1-hexene incorporation ability as determined by 13C NMR. Moreover, the short chain branch distribution (SCBD) of the copolymer obtained via the CrMo/Si catalyst was also improved as confirmed by temperature rising elution fractionation (TREF) cross successive self-nucleation and annealing (SSA) methods. The results of TREF and SSA showed that the amount of short chain branches for the copolymer was increased in the high MW part, which would benefit for the long term mechanical property of polyethylene.

Novel SiO2‐Supported Chromium Oxide(Cr)/Vanadium Oxide(V) Bimetallic Catalysts for Production of Bimodal Polyethylene

Novel SiO2‐supported Cr–V bimetallic oxides catalysts, which were capable of one‐pot synthesizing polyethylene with bimodal molecular weight distribution, had been successfully developed. These catalysts were prepared with a simple introduction of vanadium oxide onto the traditional Phillips CrOx/SiO2 catalyst. The polymerization activity over the Cr–V bimetallic catalysts was significantly improved compared with the V‐free Phillips CrOx/SiO2 catalyst. Moreover, the bimodal ethylene/1‐hexene copolymer prepared by the novel catalyst showed a better short chain branch distribution with more 1‐hexene comonomer inserted into the PE chains with high molecular weight, which would be favorable for the long term mechanical properties of the bimodal PE as potential high grade pipe materials.

Calibration curve establishment and fractionation temperature selection of polyethylene for preparative temperature rising elution fractionation

A series of copolymers of ethylene with 1-hexene synthesized using a metallocene catalyst are selected and mixed. The blend is fractionated via preparative temperature rising elution fractionation (P-TREF). All fractions are characterized via high-temperature gel permeation chromatography (GPC), C-13 nuclear magnetic resonance spectroscopy (C-13-NMR), and differential scanning calorimetry (DSC). The changes in the DSC melting peak temperatures of the fractions from P-TREF as a function of elution temperature are almost linear, thereby providing a reference through which the elution temperature of TREF experiments could be selected. Moreover, the standard calibration curve (ethylene/1-hexene) of P-TREF is established, which relates to the degree of short-chain branching of the fractions. The standard calibration curve of P-TREF is beneficial to study on the complicated branching structure of polyethylene. A convenient method for selecting the fractionation temperature for TREF experiments is elaborated. The polyethylene sample is fractionated via successive self-nucleation and annealing (SSA) thermal fractionation. A multiple-melting endotherm is obtained through the final DSC heating scan for the sample after SSA thermal fractionation. A series of fractionation temperatures are then selected through the relationship between the DSC melting peak temperature and TREF elution temperature.

Overexpression of STARCH BRANCHING ENZYME II increases short-chain branching of amylopectin and alters the physicochemical properties of starch from potato tuber.

BackgroundStarch is biosynthesised by a complex of enzymes including various starch synthases and starch branching and debranching enzymes, amongst others. The role of all these enzymes has been investigated using gene silencing or genetic knockouts, but there are few examples of overexpression due to the problems of either cloning large genomic fragments or the toxicity of functional cDNAs to bacteria during cloning. The aim of this study was to investigate the function of potato STARCH BRANCHING ENZYME II (SBEII) using overexpression in potato tubers.ResultsA hybrid SBEII intragene consisting of potato cDNA containing a fragment of potato genomic DNA that included a single intron was used in order to prevent bacterial translation during cloning. A population of 20 transgenic potato plants exhibiting SBEII overexpression was generated. Compared with wild-type, starch from these tubers possessed an increased degree of amylopectin branching, with more short chains of degree of polymerisation (DP) 6–12 and particularly of DP6. Transgenic lines expressing a GRANULE-BOUND STARCH SYNTHASE (GBSS) RNAi construct were also generated for comparison and exhibited post-transcriptional gene silencing of GBSS and reduced amylose content in the starch. Both transgenic modifications did not affect granule morphology but reduced starch peak viscosity. In starch from SBEII-overexpressing lines, the increased ratio of short to long amylopectin branches facilitated gelatinisation, which occurred at a reduced temperature (by up to 3°C) or lower urea concentration. In contrast, silencing of GBSS increased the gelatinisation temperature by 4°C, and starch required a higher urea concentration for gelatinisation. In lines with a range of SBEII overexpression, the magnitude of the increase in SBEII activity, reduction in onset of gelatinisation temperature and increase in starch swollen pellet volume were highly correlated, consistent with reports that starch swelling is greatly dependent upon the amylopectin branching pattern.ConclusionThis work reports the first time that overexpression of SBEII has been achieved in a non-cereal plant. The data show that overexpression of SBEII using a simple single-intron hybrid intragene is an effective way to modify potato starch physicochemical properties, and indicate that an increased ratio of short to long amylopectin branches produces commercially beneficial changes in starch properties such as reduced gelatinisation temperature, reduced viscosity and increased swelling volume.Electronic supplementary materialThe online version of this article (doi:10.1186/s12896-015-0143-y) contains supplementary material, which is available to authorized users.