PDMS Homopolymer Research Articles

Bottlebrush Amphiphilic Polymer Co-Networks.

We report the synthesis of novel poly(ethylene glycol) and poly(dimethyl siloxane) (PEG and PDMS, respectively) bottlebrush amphiphilic polymer co-networks (B-APCNs) with high gel fractions by a grafting-through ring-opening metathesis polymerization. By varying the volume fraction of PEG (), we alter the crystallinity of the networks, achieving complete suppression of PEG crystallinity at . Furthermore, we show that the crystallinity of these networks can be tuned to alter their moduli. Through dynamic mechanical analysis, we show that the storage and loss moduli of networks with completely suppressed crystallinity () behave similarly to a PDMS homopolymer bottlebrush network. These bottlebrush networks represent an unexplored architecture for the field of amphiphilic polymer co-networks.

Thin film confinement reduces compatibility in symmetric ternary block copolymer/homopolymer blends

ABSTRACTThe thin film phase behavior of ternary blends consisting of symmetric poly(styrene) (PS)‐b‐poly(dimethylsiloxane)(PDMS), PS, and PDMS was investigated using X‐ray reflectivity (XRR) and atomic force microscopy (AFM). This system is strongly segregated, and the homopolymers are approximately the same length as the corresponding blocks of the copolymer. The XRR and AFM data are used to quantify changes in domain spacing (L) and morphology evolution with increasing homopolymer content (Φ H). In 100 nm thick films, from Φ H = 0 to 0.20, the system maintains a perfect parallel lamellar structure and domains swell as predicted based on theory; however, from Φ H = 0.30 to 0.50, a morphology transition to a “dot pattern” morphology (tentatively identified as perforated lamellae) and mixed morphologies were observed before macrophase separation. In thicker films, dot patterns were observed for a broad range of Φ H before macrophase separation. The absence of the bicontinuous microemulsion phase reported for bulk blends and thin films of perpendicular lamellae and the presence of dot patterns/perforated lamellae are attributed to preferential migration of the PDMS homopolymer to the wetting layers located at the substrate and free air interfaces, which leads to an asymmetric composition within the film and morphology transition. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 1443–1451

Interfacial Energy-Controlled Top Coats for Gyroid/Cylinder Phase Transitions of Polystyrene-block-polydimethylsiloxane Block Copolymer Thin Films.

Block copolymers (BCPs) with a high Flory-Huggins interaction parameter (χ) can form well-defined sub-10 nm periodic structures and can be used as a template for fabrication of various functional nanostructures. However, the large difference of surface energy between the blocks commonly found in high-χ BCPs makes it challenging to stabilize a useful gyroid morphology in thin film form. Here, we used an interfacial-energy-tailored top-coat on a blended film of a polystyrene-block-polydimethylsiloxane (PS-b-PDMS) BCP and a low-molecular-weight PDMS homopolymer with a hydrophilic end functional group. The top coat consisted of a random mixture of 40% hydrolyzed poly(vinyl acetate)-random-poly(vinly alcohol) (PVA-r-PVAc, PVA40) and PVAc homopolymer. At the optimized top-coat composition, gyroid nanostructures with sub-10 nm strut width were achieved down to ∼125 nm film thickness, which is only 3 times the lattice parameter of the gyroid structure. This is in marked contrast with a mixed morphology of gyroid and cylinders obtained for other compositions of the top coat. Self-consistent field theoretic simulations were used to understand the effect of the interfacial energy between the top coat and BCP/homopolymer blends on the phase transition behavior of the BCP/homopolymer films.

Disk-Shaped Bicelles in Block Copolymer/Homopolymer Blends

Mixtures of micelle-forming and lamella-forming amphiphiles in solution can form disk-shaped bilayers, sometimes referred to as bicelles. Using self-consistent field theory (SCFT), we investigate the structure and stability of these aggregates in a blend of two species of PS-PDMS diblock with PDMS homopolymer at 225C. We find that the center of each disk is mainly composed of lamella-forming diblocks, while its thicker rim is mostly formed of micelle-forming diblocks. However, this segregation is not perfect, and the concentration of micelle formers is of the order of 10% on the flat central surface of the bicelle. We also find that the addition of micelle former to the mixture of lamella former and homopolymer is necessary for disk-like bicelles to be stable. Specifically, the free energy density of the disk has a minimum as a function of the disk radius when both micelle- and lamella-forming diblocks are present, indicating that the bicelles have a preferred, finite radius. However, it decays monotonically when only lamella former is present, indicating that the bicelle structure is always unstable with respect to further aggregation in these systems. Finally, we identify a concentration range where the bicelle is predicted to have a lower free energy density than the simple cylindrical and lamellar aggregates, and so might be thermodynamically stable.

A macromonomer approach to the synthesis of poly(1,1‐bis(ethoxycarbonyl)‐2‐vinyl cyclopropane‐graft‐dimethyl siloxane)

AbstractPoly(1,1‐bis(ethoxycarbonyl)‐2‐vinyl cyclopropane (ECVP)‐graft‐dimethyl siloxane) copolymers were prepared using a macromonomer approach. Poly(dimethyl siloxane) (PDMS) macromonomers were prepared by living anionic polymerization of cyclosiloxanes followed by sequential chain‐end capping with allyl chloroformate. These macromonomers were then copolymerized with ECVP. MALDI‐ToF mass spectrometry and 1H NMR spectroscopy were used to show that the macromonomers had approximately 80% of the end groups functionalized with allyl carbonate groups. Gradient polymer elution chromatography showed that high yields of the graft copolymers were obtained, along with only small fractions of the PECVP and PDMS homopolymers. Differential scanning calorimetry showed that the low glass transition temperature (Tg) of the PDMS component could be maintained in the graft copolymers. However, the Tg was a function of polymer composition and the polymers produced had Tgs that ranged from −50 to −120 °C. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

Block and Graft Copolymers of Poly(ethylene glycol) and Poly(dimethylsiloxane) for Blood Contacting Biomedical Materials Applications

The incorporation of both hydrophobic and hydrophilic groups into a synthetic polymer is a potent way of controlling its surface and interfacial properties. With this end result in mind, we describe herein the synthesis and characterization of poly(dimethylsiloxane-b-ethyleneoxide) block copolymers (PDMS-b-PEO) and poly(dimethylsiloxane-g-ethyleneoxide) grafted copolymers (PDMS-g-PEO). These amphiphillic copolymers were also investigated as surface modifying agents for passifying hydrophobic polymer surfaces in blood contacting applications. Specifically, the various (PDMS-b-PEO) and (PDMS-g-PEO) copolymers were coated onto poly(styrene-divinylbenzene) microspheres by their physical adsorption from solution. These surfaces were then evaluated for blood contacting applications utilizing a fibrinogen and thrombin protocol. In particular, the binding of fibrinogen and the functionality of the surface bound fibrinogen on an otherwise hydrophobic surface (polystyrene) was investigated. As the conversion of fibrinogen to fibrin is facilitated by thrombin, the aggregation of the copolymer-coated hydrophobic microspheres was followed using an optical method after the sequential exposure of the microspheres to fibrinogen and then to thrombin. We were able to determine how the adsorbed copolymers affected the functionality of the bound fibrinogen at an interface. Our hypothesis is that the hydrophobic siloxane units of the copolymers will be in close proximity to the polystyrene surface and that the PEO will extend out from the surface and therefore render the synthetic polymer system hemocompatible. Following the fibrinogen and thrombin protocol and determining the fibrinogen-dependent aggregation, the results show that the PDMS-b-PEO copolymers (having a PEO content from 4.6 to 11.5 weight %) were similar in terms of particle aggregation when compared to the pure polystyrene microspheres (blank) or to the microspheres that were coated with a linear PDMS homopolymer. By comparison, the PDMS-g-PEO copolymers (having a PEO content from 58 to 80 weight %) were seen to reduce the fibrinogen functionality on the microsphere system surface. Thus the data indicate that the PDMS-g-PEO copolymers can behave like molecular brushes that are able to pacify the surface of the hydrophobic polystyrene microspheres. A somewhat unexpected observation was that for the copolymer system having a low PEO content the fibrinogen-dependent aggregation of the otherwise hydrophobic microspheres was observed to increase relative to the pure microspheres (blank). It is clear from the findings of this investigation that the surface packing and molecular orientation of both the adsorbed copolymer and also of the fibrinogen are important factors that govern the properties and applications of blood contacting biomaterials.

Fouling release nanostructured coatings based on PDMS-polyurea segmented copolymers

The bulk and surface characteristics of a series of coatings based on PDMS-polyurea segmented copolymers were correlated to their fouling release performance. Incorporation of polyurea segments to PDMS backbone gives rise to phase separation with the extensively hydrogen bonded hard domains creating an interconnected network that imparts mechanical rigidity. Increasing the compositional complexity of the system by including fluorinated or POSS-functionalized chain extenders or through nanoclay intercalation, confers further thermomechanical improvements. In analogy to the bulk morphology, the surface topography also reflects the compositional complexity of the materials, displaying a wide range of motifs. Investigations on settlement and subsequent removal of Ulva sporelings on those nanostructured surfaces indicate that the work required to remove the microorganisms is significantly lower compared to coatings based on standard PDMS homopolymer. All in all, the series of materials considered in this study demonstrate advanced fouling release properties, while exhibiting superior mechanical properties and, thus, long term durability.

Synthesis of polystyrene microspheres by dispersion polymerization in supercritical carbon dioxide using a poly(dimethylsiloxane)-based macroazoinitiator

The synthesis of polystyrene microspheres was achieved by the dispersion polymerization of styrene in supercritical carbon dioxide using azobisisobutylonitrile (AIBN) and a poly(dimethylsiloxane) (PDMS)-based macroazoinitiator, VPS-1001. VPS-1001 contained seven to nine molecules of the azo groups and the PDMS blocks with a molecular weight of 10,000 per molecule. The polymerization in the presence of both VPS-1001 and AIBN produced polystyrene microspheres with a diameter below 4 μm in over 85% yields, whereas the polymerization with VPS-1001 in the absence of AIBN provided a nonspecific polystyrene in only 20% yield. The particle size decreased as a result of increasing the concentration of VPS-1001. It was confirmed that the polystyrene particles were stabilized by the PDMS-block-polystyrene formed through the polymerization initiated by VPS-1001 because the polymerization using a PDMS homopolymer provided nonspecific polystyrene as a precipitate during the polymerization.

Blends of a 3-Miktoarm Star Terpolymer (3μ-ISD) of Isoprene (I), Styrene (S), and Dimethylsiloxane (D) with PS and PDMS. Effect on Microdomain Morphology and Grain Size

The morphologies of a 3-miktoarm star terpolymer of isoprene (I), styrene (S), and dimethylsiloxane (D), 3μ-ISD, and its blends with PDMS and PS homopolymers, having a lower molecular weight than the corresponding blocks of the star, were studied. Combined EF-TEM and 3D electron tomography clearly revealed that three kinds of cylindrical structures, composed of three different blocks, joined to fill the space and that these cylinders were curved collectively into an arc. The grain size of this star terpolymer was extremely small compared with that of other known linear block copolymers. By blending the neat 3μ-ISD with a small quantity of PDMS homopolymer (5 wt %), the morphology remained the same, but the grain size increased dramatically. It seems that the PDMS homopolymer inserts into the PDMS phase of the star terpolymer and straightens the bent cylinders, thereby increasing long-range order. However, the extra PDMS accumulates in line defects, which if controlled could be beneficial as waveguides in photonic crystals. Blending with PS leads to smaller grain sizes and unstable hexagonal symmetry, which disappears upon the addition of extra PS. Therefore, tetragonal symmetry is inherent in the neat star.

Poly(ferrocenyldimethylsilane- b-dimethylsiloxane) microsphere with shell thickness controllable structure prepared through self-assembly

A novel approach was applied to prepare shell thickness controllable magnetic microsphere precursor through the self-assembly of PDMS homopolymer with PFS- b-PDMS in selective solvent and adjusting the prepared conditions of samples such as temperature and aging time. The magnetic microsphere precursor provided with adjustable dimension of shell thickness 15, 40 and 90 nm, respectively, which made it possessing various potential applications in biomedical and separating engineering fields.

Heterogeneity of the Segmental Dynamics of Poly(dimethylsiloxane) in a Diblock Lamellar Mesophase: Dielectric Relaxation Investigations

The segmental dynamics of amorphous poly(dimethylsiloxane) (PDMS) in a lamellar poly(styrene)−poly(dimethylsiloxane) diblock (PS−PDMS) is investigated by means of broadband dielectric spectroscopy. Because of the absence of normal mode in PDMS, we have been able to analyze the low-frequency side of the α-relaxation in detail. The characteristic time of the segmental dynamics is found to be significantly higher than that in a PDMS homopolymer. In addition, the dielectric loss peak displays a pronounced broadening in the low-frequency side as compared with that observed in pure PDMS. We showed that the ε‘ ‘(ω) curves could be well described assuming two types of PDMS segments depicting qualitatively distinct segmental dynamics. In one case, the dielectric response is similar to that one of the amorphous constrained phase in a cold-crystallized PDMS homopolymer. For the other segments, the dielectric behavior appears close to that one of an amorphous PDMS homopolymer. However, some differences remain indicating a significant gradient of mobility within this second type of PDMS segments. We explain all these findings by considering a simple picture of the PDMS segments in the PS−PDMS lamellar mesophase.

Influence of diblock copolymer on the morphology and properties of polystyrene/poly(dimethylsiloxane) blends

AbstractBlends of polystyrene (PS) and poly(dimethylsiloxane) (PDMS), with and without diblock copolymers (PS‐b‐PDMS), were prepared by melt mixing. The melt rheology behavior of the blends was studied with a capillary rheometer. The morphology of the blends was examined with scanning electron microscopy. The miscibility of the blends was studied with differential scanning calorimetry. The morphology of PS/PDMS blends was modified by the addition of PS‐b‐PDMS copolymers and investigated as a function of the molar mass of the diblock copolymers, viscosity ratios and the processing conditions. As investigated, the observed morphology of the melt‐blended PS/PDMS pair unambiguously supported the interfacial activity of the diblock copolymers. When a few percent of the diblock copolymers blended together with the PS and PDMS homopolymers, the phase size was reduced and the phase dispersion was firmly stabilized against coalescence. The compatibilizing efficiency of the copolymers was strongly dependent on its molar mass. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2747–2757, 2004

Glucose permeable poly (dimethyl siloxane) poly ( N-isopropyl acrylamide) interpenetrating networks as ophthalmic biomaterials

Poly (dimethyl siloxane) (PDMS) has been widely used as a biomaterial in ophthalmic and other applications due to its good compatibility, high mechanical strength, excellent oxygen permeability and transparency. However, for use as an artificial cornea, contact lens and in other applications, modifications with hydrophilic functional groups or polymers are necessary to improve wettability for tear protein and mucin interactions and to improve glucose permeability for cellular health. Poly ( N-isopropyl acrylamide) (PNIPAAM) is a biocompatible and hydrophilic polymer that has been extensively studied on controlled drug release applications due to its lower critical solution temperature (LCST) phenomenon. In the current work, a composite interpenetrating network (IPN) of PDMS and PNIPAAM was formed to generate polymers with oxygen and glucose permeability as well as improved wettability compared to PDMS homopolymers and greater mechanical strength than PNIPAAM homopolymers. Transparent vinyl and hydroxyl terminated PDMS/PNIPAAM IPNs (PDMS-V and PDMS-OH IPNs, respectively) were successfully synthesized. Transmission electron microscopy images verified the structure of the IPNs. Surface analysis suggested that PNIPAAM was present on the surface as well as in the bulk material. PDMS-OH IPNs generated from a PDMS-OH matrix cured in the presence of solvent had the highest glucose permeability at 10 −7 cm 2/s, comparable to that of the native cornea. The LCST phenomenon remained in these materials, although changes were not as abrupt as with pure PNIPAAM. These results suggest that these materials may be further developed as ophthalmic biomaterials or for controlled drug-release applications.

Aggregation Behavior of Short-Chain PDMS-b-PEO Diblock Copolymers in Aqueous Solutions

Short-chain poly(dimethylsiloxane)−poly(ethylene oxide) (PDMS-b-PEO) diblock copolymers with different ratios of the hydrophilic to hydrophobic segments were synthesized via coupling of end-functionalized PDMS and PEO homopolymers. Their aggregation behavior was investigated by tensiometry, fluorescence, and cryogenic transmission electron microscopy. Interestingly, the critical aggregation concentration of the surfactants increased with increasing length of the hydrophobic chain. The electron microscopy studies showed that the surfactants preferentially aggregate into vesicles and lamellar structures.

The Order−Disorder Transition and the Disordered Micelle Regime for Poly(ethylenepropylene-b-dimethylsiloxane) Spheres

Two asymmetric poly(ethylenepropylene-b-dimethylsiloxane) diblock copolymer melts have been examined by rheology, small-angle X-ray scattering (SAXS), and small-angle neutron scattering (SANS). The two copolymers have total molecular weights of 24 400 and 23 900 and PDMS volume fractions of 0.12 and 0.10, respectively. The latter copolymer was obtained by extensive fractionation of the former, the difference in composition arising primarily from the removal of traces of PDMS homopolymer. The order−disorder transition (ODT) is unambiguously identified by rheology and SAXS. Above the ODT the SANS and rheological properties are consistent with the recently proposed disordered micelle regime, whereby the copolymers are associated in micellar aggregates that are not ordered on a lattice. The viscosity of the melt in this regime is greater than that of a poly(ethylenepropylene) homopolymer of the same total molecular weight. The SANS structure factors were analyzed by a generalized inverse Fourier transform and by direct fitting to a model based on the Percus−Yevick structure factor and either a spherical or an ellipsoidal form factor. Both approaches give comparable results, and the average micelle core radius, effective hard-sphere radius, and volume fraction were extracted as a function of temperature. The fitting suggests that as temperature increases the micelles remain relatively unchanged, but their number density and volume fraction decrease steadily. The fractionated copolymer has a significantly smaller micellar core than its precursor and therefore a significantly smaller aggregation number. These differences are attributable to the partitioning of PDMS homopolymer into the micellar cores. For these samples the critical micelle temperature (cmt), where the volume fraction of micelles should become negligible, was not accessed, even 100 deg above the ODT.

A pulsed field gradient nuclear magnetic resonance study of a ternary homopolymer/diblock copolymer blend in the bicontinuous microemulsion phase

Pulsed field gradient (PFG) nuclear magnetic resonance (NMR) was applied to study self-diffusion in a ternary blend containing equal molar volumes of the homopolymers poly(dimethylsiloxane) (PDMS) and poly(ethylethylene) (PEE), and the nearly symmetric PDMS-PEE diblock copolymer. The blend forms a bicontinuous microemulsion (BμE) below ∼83 °C, while it is in the disordered state at higher temperatures. PFG NMR has also been applied to the individual components of the blend. In the blend, we find one diffusional process in the disordered state and two diffusional processes in the BμE state. The fast process in the BμE is due to the diffusion of the PDMS homopolymers through the BμE. This diffusion is ten times slower than that of bulk PDMS at the same temperature, indicating restricted diffusion of PDMS in the BμE. The diffusion coefficient of the slower process in the ternary blend is slightly increased compared with bulk PEE. It is tentatively assigned to PEE self-diffusion. The changes in homopolymer diffusivities are semiquantitatively explained in terms of a model taking into account the tortuosity of the BμE as well as the fast exchange of homopolymers between the domains and the difference in viscosities of the PEE and the PDMS domains. Our results are compared with data obtained previously on the identical sample with dynamic light scattering experiments [T. L. Morkved et al., Faraday Discuss. 112, 335 (1998)].

Block copolymer compatibilizers for polystyrene/poly(dimethylsiloxane) blends

AbstractSymmetric polystyrene (PS)–poly(dimethylsiloxane) (PDMS) diblock copolymers were mixed into a 20% dispersion of PDMS in PS. The effect of adding the block copolymer on the blend morphology was examined as a function of the block copolymer molecular weight (Mn,bcp), concentration, and viscosity ratio (ηr). When blended together with the PS and PDMS homopolymers, most of the block copolymer appeared as micelles in the PS matrix. Even when the copolymer was preblended into the PDMS dispersed phase, block copolymer micelles in the PS matrix phase were observed with transmission electron microscopy after mixing. Adding 16 kg/mol PS–PDMS block copolymer dramatically reduced the PDMS particle size, but the morphology, as examined by scanning electron microscopy, was unstable upon thermal annealing. Adding 156 kg/mol block copolymer yielded particle sizes similar to those of blends with 40 or 83 kg/mol block copolymers, but only blends with 83 kg/mol block copolymer were stable after annealing. For a given value of Mn,bcp, a minimum PDMS particle size was observed when ηr ∼ 1. When ηr = 2.6, thermally stable, submicrometer particles as small as 0.6 μm were observed after the addition of only 3% PS–PDMS diblock (number‐average molecular weight = 83 kg/mol) to the blend. As little as 1% 83 kg/mol block copolymer was sufficient to stabilize a 20% dispersion of 1.1‐μm PDMS particles in PS. Droplet size reduction was attributed to the prevention of coalescence caused by small amounts of block copolymer at the interface. The conditions under which block copolymer interfacial adsorption and interpenetration were facilitated were explained with Leibler's brush theory. © 2002 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 346–357, 2002; DOI 10.1002/polb.10098

Determination of Molecular Weight of PDPS Modified Copolymers

AbstractMolecular weight (MW) determinations of polydiphenylsiloxane‐co‐polydimethylsiloxane (PDPS/PDMS), polydiphenylsiloxane‐co‐polymethylphenylsiloxane (PDPS/PMPS) and polydiphenylsiloxane‐co‐polymethyl(3,3,3‐trifluoropropyl)siloxane (PDPS/PMFPS) statistical copolymers by gel permeation chromatography (GPC), GPC coupled differential viscometer (GPC‐DV) and light scattering (LS) techniques have been compared and discussed. The MW obtained by GPC‐DV in the PDPS/PDMS and the PDPS/PMPS series agreed with that obtained by LS very well. In PDPS/PDMS copolymers, it was found that the MW obtained by GPC was much lower than that obtained by GPC‐DV and LS, as Ph2SiO) content is higher than 50 mol%. In PDPS/PMFPS copolymers, the MW obtained by GPC was far different from that obtained by GPC‐DV and the deviation decreased with increasing Ph2SiO) mol%. The α values of the copolymers can be explained by the structure of the polymer in tetrahydrofuran (THF). Based on the relatively soluble copolymers, not only the differential refractive index increments (dn/dc) of PMPS, PDMS and PMFPS homopolymers but also that of the PDPS homopolymer in THF could be calculated by their corresponding copolymers.

Novel Functional Polymers: Poly(dimethylsiloxane)−Polyamide Multiblock Copolymer. 8. Surface Studies of Aramid−Silicone Resin by Means of XPS, Static SIMS, and TEM

The surface structures of solvent-cast films with aramid−poly(dimethylsiloxane) (poly(dimethylsiloxane) = PDMS) multiblock copolymers (PASs) that contained 8, 14, 24, 41, and 71 wt % of PDMS were characterized by angular-dependent X-ray photoelectron spectroscopic (XPS) measurements, static secondary ion mass spectrometric (SSIMS) measurements, and transmission electron microscopic (TEM) observations. The results of angular-dependent XPS measurement elucidated that the surface concentration of the PDMS segments was much higher than that in bulk and further increased with a decrease in the sampling depth. In particular, the Si/C ratios that were determined by XPS at a 10° takeoff angle in PAS films that contained more than 24 wt % PDMS were almost the same as that in the PDMS homopolymer. From the results of SSIMS measurement, the outermost surfaces of all of the PAS films were found to be completely covered with a PDMS segment even if the PDMS content was only 8 wt % in bulk. In addition, we visually confirmed the surface enrichment of the PDMS segment by TEM observation. The free surfaces of all PAS films were predominantly covered with a PDMS thin layer, although the microphase-separated structures in bulk were different according to the PDMS content in PAS.

Determination of the Distribution of Poly(dimethylsiloxane) Segment Lengths at the Surface of Poly[(dimethylsiloxane)−urethane]-Segmented Copolymers by Time-of-Flight Secondary Ion Mass Spectrometry

Time-of-flight secondary ion mass spectra were recorded from submonolayer thin films of aminopropyl end-capped poly(dimethylsiloxane) (PDMS) and from thick films (ca. 50 μm) of poly[(dimethylsiloxane)−urethane] (PU−DMS)-segmented copolymers. Ions detected and assigned to fragments in the low-mass range (m/z ≤ 300) provided structural information about the repeat units and the end groups. The high-mass spectrum of the PDMS homopolymer yielded a series of ions assigned to Ag+-cationized oligomers; this enabled determination of the molecular weight distribution in comparison with GPC measurement. In the high-mass (m/z = 800−3500) spectra of thick PU−DMS films, the peak series was assigned to a simple fragmentation process. That process would yield ions where the intact PDMS segment is present; it therefore can be used to evaluate the PDMS segment length distribution at the surface of the copolymer. It was found that the distribution of PDMS segment lengths segregated at the surface of the thick film was almo...