Grafting and crosslinking

The most important practical application of the organometallic complex photoinitiators is the possibility of using these types of initiators in modifying the pre-existing polymer chain, e.g., block, graft, and crosslinked copolymers preparation. 

A similar type of condensation between a hydroxyl-containing polymer (such as secondary cellulose acetate) with VO(BrC6H4N=CHO CfiH4)2 CUVOL2CI] produces photoactive polymers [68]. When irradiated with UV light in the presence of styrene or MMA, grafted and crosslinked polymers were obtained ... 

Polyepichlorohydrin (PECH) is well known as a reactive elastomer. Displacement at the carbon-chlorine bond of PECH has been accomplished with a wide variety of nucleophilic reagents, for the purposes of polymer modification, grafting and crosslinking (1, 2). On the other hand, the PECH structure (1) is hardly optimal from the point of view of its reactivity as a substrate for nucleophilic... 

Meier MAR, Schubert US. Terpyridine-modified poly(vinyl chloride) possibilities for supramolecular grafting and crosslinking. J Polym Sci Part A Polym Chem 2003 41 2964-2973. 

The properties of impact polystyrene can be improved by simultaneous grafting and crosslinking upon rubber. Changing cis-polybutadiene into trans-polybutadiene and eliminating the 1,2-vinyl configuration through radiation are discussed by Parkinson. 

Seko, N., Tamada, M. and Yoshii, F. (2005) Current status of adsorbent for metal ions with radiation grafting and crosslinking techniques. Nuclear Instruments and Methods in Physics Research, Section B Beam Interactions with Materials and Atoms, 236(1-4), 21-29. 

Returning to Vollmert s patent (18), we apply the more complete spectrum of operations to his example 1. In this case butyl acrylate and acrylic acid are dissolved in acetone with azoisobutyronitrile (initiator) and dodecyl mercaptan (chain transfer agent), polymerized, and the acetone is evaporated to form polymer 1. Separately, styrene and 1,4-butanediol monoacrylate are bead polymerized with benzoyl peroxide to form polymer 2. Polymers 1 and 2 are mechanically blended with the simultaneous addition of 1,4-butanediol followed by heating to promote grafting and crosslinking. These steps can be represented in some detail by ... 

Other important factors include monomer sequence distribution, distribution of graft and crosslink sites along the chains, the occurrence of branching per se, and the general phenomena of side reactions. In addition, stirring rate, the detailed post-reaction "workup procedure, the temperature history, subsequent processing and fabrication conditions, etc. must be considered since these have major effects on the nature of the product. 

When external forces act on HIPS, the rubber particles have a stress-relaxing action. To do this job, they must be bound sufficiently to the matrix and have a certain elasticity. This means that the rubber used must be capable of grafting and crosslinking. Both properties can be controlled within certain limits via the microstructure. These requirements mean that nowadays use is predominantly made of medium-m and sometimes also high-cw rubbers, which can be produced using organolithium initiators or coordinate Ziegler catalysts. 

Grafting and crosslinking influence the transition temperature of polymers. As an example, it was observed that for cellulose triacetate or secondary cellulose acetate the glass transition increased with increasing molecular mass of the poly(methylmethacrylate) or poly(methacrylic add) grafted chain [42]. 

All the above calculations have assumed x values independent of concentration, grafting, and crosslinking. In high impact polystyrene, all three factors can be important. 

The diameter of the polybutadiene latex particles used in ABS synthesis usually ranges from 0.1 ju to lju, and the polymer is always crosslinked within the particles. Consequently, after grafting, every polybutadiene particle becomes a particle of grafted and crosslinked polymer which is much heavier than the linear copolymer molecules. 

The reaction proceeds via grafting and crosslinking of the elastomer after the reaction is complete, the elastomer is dispersed as particles in the reaction mass. Because of the side chains, these particles adhere to the matrix, and, through a mechanism that is not yet completely clear, they increase the plas-tomer tenacity which is high even at temperatures below zero. 

Morphological examination of the reaction products also provided evidence that, with EPDM elastomers, the grafted and crosslinked rubber remained dispersed in the matrix as particles with an average diameter of 2-5(i. The structure remained unaltered, even after mechanical actions such as those required for transformation into manufactured articles. On the other hand, with EP rubbers, particle morphology was markedly altered under the same transformation conditions. 

Interesting blends, having a broad range of properties, were prepared in two steps 1. BR was grafted and crosslinked with either styrene or methylmethacrylate to produce a core-shell copolymer. 2. Next, it was blended with PO for improved processability, impact resistance, rigidity, etc. [Aoyama et al., 1993, 1994]. Structural blends of styrene-grafted PP with either SBR, SBS, or an acrylic elastomer were developed [DeNicola andConboy, 1994]. 

Covalent grafting and crosslinking that result in high molecular weights copolymers. 

Companies that practice the graft technology include Quantum Chemicals. Cable processors that practice both graft and crosslink technology include BICC, Alcan, and Okonite. 

An interpenetrating polymer network (IPN) is defined as a combination of two crosslinked polymers, at least one of which has been synthesised [98] and/or crosslinked in the immediate presence of the other. From the topological point of view, IPNs are closely related to pol)nner blends and to block, graft and crosslinked copolymers. From the synthesis point of view, IPNs can be classified, broadly, into two general types (a) sequential IPNs where a polymer network is formed which is then swollen by the monomer, plus a crosslinking agent and an activator, which is then polymerised in situ to form the second network and (b) simultaneous IPNs (SIPN) where the components necessary to form both networks are mixed and polymerised, at the same time, by non-competing mechanisms. If one of the two polymers is linear (uncrosslinked), a semi-IPN results. A homo-IPN results if both the network polymers are identical in chemical composition [98]. 

Ranogajec, F. Effect of solvent on radiation grafting and crosslinking of polyethylene. Radiat. Phys. Chem. 76, 1381-1384 (2007)... 

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