Free Radical Bulk Copolymerization Research Articles

Mechanism-Guided Discovery of Cleavable Comonomers for Backbone Deconstructable Poly(methyl methacrylate).

The development of cleavable comonomers (CCs) with suitable copolymerization reactivity paves the way for the introduction of backbone deconstructability into polymers. Recent advancements in thionolactone-based CCs, exemplified by dibenzo[c,e]-oxepine-5(7H)-thione (DOT), have opened promising avenues for the selective deconstruction of multiple classes of vinyl polymers, including polyacrylates, polyacrylamides, and polystyrenics. To date, however, no thionolactone CC has been shown to copolymerize with methacrylates to an appreciable extent to enable polymer deconstruction. Here, we overcome this challenge through the design of a new class of benzyl-functionalized thionolactones (bDOTs). Guided by detailed mechanistic analyses, we find that the introduction of radical-stabilizing substituents to bDOTs enables markedly increased and tunable copolymerization reactivity with methyl methacrylate (MMA). Through iterative optimizations of the molecular structure, a specific bDOT, F-p-CF3PhDOT, is discovered to copolymerize efficiently with MMA. High molar mass deconstructable PMMA-based copolymers (dPMMA, Mn > 120 kDa) with low percentages of F-p-CF3PhDOT (1.8 and 3.8 mol%) are prepared using industrially relevant bulk free radical copolymerization conditions. The thermomechanical properties of dPMMA are similar to PMMA; however, the former is shown to degrade into low molar mass fragments (<6.5 kDa) under mild aminolysis conditions. This work presents the first example of a radical ring-opening CC capable of nearly random copolymerization with MMA without the possibility of cross-linking and provides a workflow for the mechanism-guided design of deconstructable copolymers in the future.

Methyl methacrylate-styrene copolymers prepared by utilizing the Trommsdorff effect in an inverted two-stage extruder

In this work, the influence of initial viscosity on the Trommsdorff effect was firstly investigated, and it was confirmed that 1000 ± 100 Pa · s of viscosity could be a criterion of the Trommsdorff effect. On this basis, a new inverted two-stage extruder was established, the designed ‘blocking unit’ was introduced to the screw configuration, and then the continuous bulk copolymerization of methyl methacrylate (MMA) and styrene (St) was carried out. The results showed that the blocking unit could effectively enhance the residence time of copolymerization, and make the molecular weight distribution of copolymer more uniform. The position of the Trommsdorff effect in the extruder was then determined by the thermal effect of copolymerization, and the mixed monomers were continuously added to effectively utilize the Trommsdorff effect. As a result, the MMA-St copolymers with high molecular weight and narrow distribution were prepared via reactive extrusion, which possessed higher melt flow rate and better thermal stability than pure-PMMA. The present work provides important reference and guidance for the industrialization of bulk free radical copolymerization via reactive extrusion.

Investigation of the mechanical and thermal properties of reactive AAEM-co-MMA adhesive

The effect of acetoacetoxyethyl methacrylate (AAEM) comonomer was investigated on the adhesion and thermal and mechanical properties of methyl methacrylate (MMA) reactive adhesive. The free radical bulk copolymerization of AAEM-co-MMA at ambient temperature was carried out in the presence of redox couple of benzoyl peroxide (BPO) and N,N-dimethylaniline (DMA). The glass transition temperature (Tg) and Young’s modulus of different AAEM comonomer compositions were investigated by dynamic mechanical thermal analysis (DMTA) and three-point bending test. The presence of AAEM comonomer resulted in a low Tg and high modulus adhesive. The results from tensile test and lap shear strength showed the usefulness of AAEM in MMA adhesive with an optimum AAEM contribution of 20 wt.%. The improvements in adhesive main properties and thermal stability may be well attributed to the formation of cross-linking bonds which is in agreement with the results of FTIR spectroscopy.

Aluminum triflate-cocatalyzed radical copolymerization of styrene and ethyl acrylate

Various random copolymers, poly(styrene-co-ethyl acrylate), were synthesized by free radical bulk copolymerization cocatalyzed by aluminum triflate (Al(OTf)3). The experimental conditions for the polymerization reactions, which include the amount of cocatalyst, polymerization time and ratio of styrene to ethyl acrylate, were investigated. The copolymer molecular weights were determined by gel permeation chromatography coupled to multi-angle laser light scattering. Compositional analysis was performed using proton nuclear magnetic resonance spectrometry. Electron paramagnetic resonance spectroscopy was also used to study the radical species which form in the presence or absence of Al(OTf)3. Kinetic studies were performed by determining monomer conversions as a function of time on gas chromatography. It was found that Al(OTf)3 accelerated the rate of polymerization significantly while also increasing the polymer molecular weights for a given conversion compared to the reactions where the triflate was absent. Al(OTf)3 can be a significantly more cost-effective and abundant alternative polymerization cocatalyst compared to some of the rare lanthanide triflates.

Transformation of the molecular structure of butyl methacrylate/acrylamide/acrylic acid copolymers during heat treatment

High-performance butyl methacrylate/acrylamide/acrylic acid (BMA/AM/AA) copolymers, being the precursor of PMI foam, were synthesized by free radical bulk copolymerization. Transformation of the molecular structures of AM/AA copolymers, BMA/AM copolymers and BMA/AM/AA copolymers was deeply investigated by use of 13C and 1H NMR, FTIR, DSC, TGA, DMA and mechanical property test. Results confirmed the occurrence of BMA/AM/AA copolymers. It tends to indicate the cyclization and cross-linking reactions during heat treatment, which would further induce the cyclic structures and cross-linking structures. A higher treatment temperature would result in a higher degree of cyclization and cross-linking. These findings confirmed the transformation of the molecular structures during heat treatment, which may be the key to improving the properties of BMA/AM/AA copolymers.

Supramolecular Polymer Networks Made by Solvent-Free Copolymerization of a Liquid 2-Ureido-4[1H]-pyrimidinone Methacrylamide

Supramolecular polymer networks based on polyacrylates with hydrogen bonding 2-ureido-4[1H]-pyrimidinone (UPy) side chains are of considerable interest due to the stimuli-responsive nature imparted by the reversible cross-links formed by dimerized UPy groups. Previously reported UPy-containing acrylic monomers are solid and show limited miscibility with comonomers, and this has stifled their (co)polymerization in bulk. We here report the synthesis of a liquid 2-ureido-4[1H]-pyrimidinone methacrylamide (UPy-OPG-MAA), which was made by connecting the UPy motif and methacrylamide (MAA) via an amine-terminated oligo(propylene glycol) (OPG) linker. The new monomer was miscible with conventional methacrylates. This permitted the photoinitiated free-radical bulk copolymerization with hexyl methacrylate (HMA) to afford a series of copolymers (poly(UPy-OPG-MAA-co-HMA)) in which the UPy-OPG-MAA content was varied between 0 and 20 mol %. The investigation of the mechanical properties of these copolymers by dynamic m...

The molecular structure control of butyl methacrylate/acrylamide (co)polymers

Butyl methacrylate (BMA)/acrylamide (AM) (co)polymers were synthesized through free radical bulk copolymerization by two steps. Effect of synthesis process on the molecular structure and properties of BMA/AM (co)polymers was deeply investigated. 13C NMR results indicated that AM only participated in copolymerization with BMA, which would be promoted under a higher prepolymerization temperature. A higher conversion ratio of AM could be obtained by batch feeding. FTIR results showed that a higher prepolymerization temperature or batch feeding could increase the content of AM unit in the BMA/AM (co)polymers. DMA results indicated that a higher prepolymerization temperature or batch feeding would induce a higher Tg value of the BMA/AM (co)polymer. DSC and TGA results showed a weight loss at 150–250°C because of the imidization reactions, which would be increased by a higher prepolymerization temperature or batch feeding. Mechanical properties of PMI foam would increase under a higher prepolymerization temperature or batch feeding. In a word, the molecular structure and properties of the BMA/AM (co)polymers could be controlled.

Copolymerization of Limonene with n‐Butyl Acrylate

The bulk free radical copolymerization of d‐limonene (Lim) with n‐butyl acrylate (BA) was carried out at 80 °C using benzoyl peroxide as initiator. Low conversion experiments were run to estimate the copolymer reactivity ratios as rBA = 6.07 and rLim = 0.0067. High conversion experiments were then conducted to validate the reactivity ratios for prediction of cumulative copolymer composition. The presence of allylic hydrogen in d‐limonene caused a notable degradative chain transfer reaction which greatly impeded polymerization. Increasing d‐limonene fractions in the copolymer resulted in a decrease in final conversion and molecular weight, and an increase in glass transition temperature.

Copolymerization of 2-Ethylhexyl Acrylate and D-Limonene

The bulk free radical copolymerization of D-limonene and 2-ethylhexyl acrylate (EHA) was conducted at 80°C using benzoyl peroxide (BPO) as initiator. Low conversion experiments were conducted to estimate the copolymer reactivity ratios. The reactivity ratios r1 = 6.896 and r2 = 0.032 (1 = EHA, 2 = d-limonene) were obtained using a non-linear, error-in-variables method with the RREVM computer program. High conversion experiments were performed and revealed that a degradative chain transfer mechanism for D-limonene dominated the polymerization.

Copolymerization of n‐Butyl Methacrylate and D‐Limonene

AbstractThe bulk free radical copolymerization of n‐butyl methacrylate (BMA) and D‐limonene is carried out at 80 °C using benzoyl peroxide (BPO) as initiator. Low conversion experiments are conducted to estimate the copolymer reactivity ratios while full conversion runs are performed to verify the estimates and to achieve high monomer conversions. Reactivity ratios of r1 = 6.0957 and r2 = 0.0459 (1 = BMA, 2 = D‐limonene) are obtained using a nonlinear, error‐in‐variables method with the RREVM computer program. Full conversions and reasonably high molecular weights are achieved at high BMA feed concentrations. Achieving high conversion is limited by a degradative chain transfer mechanism due to the D‐limonene.

Strong Cation Exchange with Innocence: Synthesis and Characterization of Borate Containing Resins and Macroporous Monoliths

Strong cation-exchange resins featured by a low loading of noncoordinating BF3– or B(C6H5)3– anions in styrene–divinylbenzene matrices at various cross-linking degrees were synthesized via free-radical bulk copolymerization with the appropriate borate monomers. The polymerization mixture was tailored to obtain swellable materials for use as insoluble carriers of single-site heterogeneous catalysts. The parent macroporous monolith was also prepared for direct use in continuous flow applications showing excellent hydrodynamic properties and high chemical and mechanical stability. All resins were carefully characterized in the solid state, and their ability to immobilize molecular metal complexes was demonstrated.

Novel Glycopolymers Based on d-Mannose and Methacrylates: Synthesis, Thermal Stability and Biodegradability Testing

This paper presents the synthesis, thermal stability and biodegradability of new d-mannose glycopolymers. These glycopolymers have been obtained by free radical bulk copolymerization of d-mannose based glycomonomer, 1-O-(2′-hydroxy-3′-methacryloyloxypropyl)-2,3:5,6-di-O-isopropylidene-d-mannofuranose (Mm), and respectively d-mannose derived oligomer (Mo) with methyl methacrylate and respectively 2-hydroxypropyl methacrylate. The chemical structures of Mm and Mo have been confirmed via FTIR, 1H-NMR and HPLC–MS spectroscopy. The copolymerization process has been investigated using differential scanning calorimetry, which allowed calculating the activation energies by applying Kissinger–Akahira–Sunose method. The glycopolymers are thermally stable, fact assessed by TG analysis; their glass transition temperature exceeds 50 °C, so they are part of the glassy class of polymers. The biodegradability of these glycopolymers has been investigated in vitro, using pure cultures of Zymomonas mobilis and Trichoderma reesei. The glycopolymers lose up to 55 % weight in just 14 days of incubation as their surface and composition is altered by colonies of microorganisms that grow on/into them, fact demonstrated using SEM/EDX.

Synthesis and Properties of Siloxane-Containing Hybrid Hydrogels with &lt;I&gt;α&lt;/I&gt;,&lt;I&gt;ω&lt;/I&gt;-Functionalized Macromers

Siloxane-containing transparent hybrid hydrogels, coupled with high oxygen permeability and moderate equilibrium water content (EWC), were successfully obtained through free radical bulk copolymerization of hydrophobic and hydrophilic monomers. Due to obvious incompatibility of hydrophobic tris(trimethylsiloxy)-3-methacrryloxypropylsilane (TRIS) and hydrophilic 2-hydroxyehtyl methacrylate (HEMA) or N-vinyl pyrrolidone (NVP) monomers, alpha,omega-methacrylate terminated poly(dimethyl siloxane) (PDMS) macromer was employed as a compatibilizer in the formulations, resulting in high optical transmittance (> 90% at 400 nm) of the hybrid hydrogels. Although properties such as EWC and oxygen permeability of the hybrid hydrogels could be tailored over a wide range, the formulations with the PDMS macromer could not increase both EWC and oxygen permeability of the hybrid hydrogels without sacrificing one of them. For controlling these two properties simultaneously, an amphiphilic alpha,omega-methacrylate terminated PEO-PDMS-PEO triblock copolymer was synthesized as a surface-active macromer, and showed its usefulness in controlling phase separation and improving oxygen permeability and EWC, at the same time, of the hybrid hydrogels.

The Luminescence Property Study of CdTe/PMMA Emitting Green Light under Visible Light

The polymerizable monomer encapsulating CdTe quantum dot was synthesized by the electrostatic reaction. Then CdTe/PMMA was successfully obtained via free radical bulk copolymerization with the mixture of the polymerizable monomer and methyl methacrylate, which emit green light under visible light. The structure and optical properties of CdTe/PMMA were investigated by Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), Uv-vis absorption spectrum, and fluorescence spectrum, respectively. The results indicated that the CdTe/PMMA emit green light under ultraviolet and visible region (380-500nm). When the polymerizable monomer encapsulating CdTe quantum dot was 1.2%, the fluorescence quantum yield of CdTe/PMMA was 7.1%.

Theoretical consideration of bulk free-radical copolymerization with allowance for the preferential sorption of monomers into globular nanoreactors

The thermodynamics of a globular solution of binary copolymer in two-component solvent is theoretically considered. Classification of phase diagrams of such a solution is performed by their topological appearance. Based on the thermodynamic theory, binary bulk free-radical copolymerization under low conversions is examined in systems where macroradicals being in globular conformational state represent isolated nanoreactors. The theoretical results achieved permit an explanation of all qualitative peculiarities observed experimentally under copolymerization in such anomalous systems.

Study on Synthesis and Chloramphenicol Release of Poly(2-hydroxyethylmethacrylate-co-acrylamide) Hydrogels

In this article, poly(2-hydroxyethylmethacrylate-co-acrylamide) hydrogels were synthesized by bulk free-radical copolymerization of 2-hydroxyethylmethacrylate (HEMA) and acrylamide (AAm) for soft contact lens(SCL)-based ophthalmic drug delivery system. The copolymer was characterized with FT-IR and SEM, the swelling property of the hydrogels were studied by gravimetrical method, and chloramphenicol was used as a model drug to investigate drug release profile of the hydrogels. The results showed that poly(2-hydroxyethylmethacrylate- co-acrylamide) hydrogels were transparent and useful SCL biomaterial, the water content increased as AAm content increase and pH decrease, and in the same way, hydrogel composition affected chloramphenicol release process too. Migration rate of chloramphenicol increased as the AAm content in the hydrogels increased in the first stage of diffusion process, whereas there was no significant difference thereafter.

Swelling behaviors, tensile properties and thermodynamic interactions in APS/HEMA copolymeric hydrogels

A series of hydrogels was synthesized from hydrophobic allyl phenyl sulfone (APS) and hydrophilic 2-hydroxyethyl methacrylate (HEMA) by bulk free radical copolymerization. The effects of APS content and temperature were studied on network parameters such as effective crosslink density (ve), molar mass between crosslinks (Mc) and polymer-water interaction parameter (x) of hydrogels. The increase in APS content was shown to enhance hydrophobic bonding within hydrogel, leading to the decrease in equilibrium water content (EWC) and the increase in volume fraction of polymer in hydrogel (ϕ2), tensile strength and Young’s modulus. At the same time, the increases in ve and x and the decrease in Mc were also observed. When the temperature is increased from 273 to 343 K, the hydrogel A/H3 undergoes decreasing in EWC and increasing in ϕ2 and x values. The thermody namic analysis indicated that the swelling process is an exothermic process.

Monomer reactivity ratios for lauryl methacrylate–isobutyl methacrylate in bulk free radical copolymerization

AbstractStatistical copolymers of isobutyl methacrylate and lauryl methacrylate were prepared by free radical bulk copolymerization at 70 °C using 2,2′‐azobisisobutyronitrile as initiator. The synthesis of these copolymers was investigated over a wide composition range at low conversion levels. Copolymer compositions were determined from the C, H and O contents obtained by elemental analysis. The monomer reactivity ratios and the 95% individual confidence intervals and 95% joint confidence intervals were calculated by the Fineman–Ross, Ezrielev–Brokhina‐Roskin, Kelen and Tüdös, Extended Kelen and Tüdös methods and a linear iterative method proposed by Mao and Huglin. The estimation process was performed by applying non‐linear techniques based on Marquardt optimization, ordinary least‐squares (OLS) and generalized least‐squares approaches and the results were compared. Monomer reactivity ratios and monomer partition coefficients were also analysed on the basis of the bootstrap models by applying the non‐linear least‐squares approach. Good agreement between experimental and calculated copolymer compositions was obtained. The results show that this copolymerization system is strictly describable by the simple bootstrap terminal model (SBTM) and accurate monomer reactivity ratios can be obtained. The monomer sequence distributions were also calculated using the monomer reactivity ratios obtained from SBTM. Copyright © 2003 Society of Chemical Industry

A Generalized Least Square Model for the Determination of Monomer Reactivity Ratios in Free Radical Copolymerization Systems

AbstractThe reliable estimation of monomer reactivity ratios is a key problem in the development of process models, and, thus, is an important issue in both process design and control. Copolymers of isobutyl methacrylate (i‐BMA), and lauryl methacrylate (LMA) were prepared by free radical bulk copolymerization at 70 °C using 2,2′–azobisisobutyronitrile (AIBN) as initiator. The monomer reactivity ratios as well as the 95% confidence intervals were calculated from Fineman‐Ross, Ezrielev‐Brokhina‐Roskin, Kelen &amp; Tudos, extended Kelen &amp; Tudos and a linear iterative method proposed by Mao and Huglin. The estimation process was performed by applying nonlinear techniques based on Marquardt optimization, “ordinary least square” (OLS) and “generalized least square” (GLS) approaches and the results were compared with each other. The novel GLS estimator program developed during this study was employed to ascertain the shape of the copolymer composition curve and good agreement between experimental and calculated copolymer composition was obtained. Also, both real and simulated data was presented, which show GLS method is a statistically valid technique for estimating reactivity ratios by accounting response error structure. This new estimation method handles regression models with error terms that are heteroskedastic or serially correlated, or both.95% joint confidence interval for reactivity ratios from “NLLS” analysis.magnified image95% joint confidence interval for reactivity ratios from “NLLS” analysis.

The copolymerization of N-vinyl-2-pyrrolidone with 2-hydroxyethyl methacrylate

The bulk free radical copolymerization of 2-hydroxyethyl methacrylate (HEMA) with N-vinyl-2-pyrrolidone (VP) was carried out to low conversions at 50 °C, using benzoyl peroxide (BPO) as initiator. The compositions of the copolymers were determined using 13C NMR spectroscopy. The conversion of monomers to polymers was studied using FT-NIR spectroscopy in order to predict the extent of conversion of monomer to polymer. From model fits to the composition data, a statistical F-test revealed that the penultimate model describes the copolymerization better than the terminal model. Reactivity ratios were calculated by using a non-linear least squares analysis (NLLS) and r H = 8.18 and r V = 0.097 were found to be the best fit values of the reactivity ratios for the terminal model and r HH = 12.0, r VH = 2.20, r VV = 0.12 and r HV = 0.03 for the penultimate model. Predictions were made for changes in compositions as a function of conversion based upon the terminal and penultimate models.