Poly growth mechanism

Direct transformation from 2,5-DSP to poly-2,5-DSP through 2,5-DSP oligomer in the crystal is shown in Scheme 1. This new reaction was named a four-centre-type photopolymerization. As well as being the first example of a topochemical reaction in a pure sense, the four-centre-type photopolymerization of 2,5-DSP crystals was the first example of photopolymerization via a step-growth mechanism. 

After the first dehydration step, the reaction propagates by successive dehydration-methanolation steps, competing with poly-merization-cyclization-aromatization processes. The existence of dehydration-methanolation mechanism is inferred from the constant presence of a small amount of methanol (from in situ C-NMR observation) on the catalyst. Further evidence has been acquired in favor of the carbenium ion chain-growth mechanism from the l C-NMR study of CO incorporation into the products during the conversion of methanol (46). 

Hence, cation-radical copolymerization leads to the formation of a polymer having a lower molecular weight and polydispersity index than the polymer got by cation-radical polymerization— homocyclobutanation. Nevertheless, copolymerization occnrs nnder very mild conditions and is regio-and stereospecihc (Bauld et al. 1998a). This reaction appears to occnr by a step-growth mechanism, rather than the more efficient cation-radical chain mechanism proposed for poly(cyclobutanation). As the authors concluded, the apparent suppression of the chain mechanism is viewed as an inherent problem with the copolymerization format of cation-radical Diels-Alder polymerization. ... 

The co-occurrence of nucleation and spinodal decomposition had been observed in the temperature quench experiment of poly(2,6-dimethyl-l,4-phenylene oxide)-toluene-caprolactam system, [64,65], in which the typical morphology formed by nucleation and growth mechanism was observed with electron-microscopy when the quench of temperature is slightly above the spinodal boundary. On the other hand, if the quench temperature is somewhat lower than the spinodal boundary, they observed interconnected structures as well as small droplets. 

The stereocomplex formation of PLLA and PDLA is enhanced in the presence of stereoblock poly(lactic acid) [419], Stereocomplex formation was proposed to be a novel method of controlling the protein- and cell-adhesive properties of biodegradable matrices composed of PEG-PLA copolymers [420], A triangular growth mechanism was proposed for the PLLA/PDLA stereocomplex [95], and the nucleating mechanism is not altered by the PLLA/PDLA blending ratio [421],... 

An alternative approach is the so-called hypergrafting that relies on the use of a linear block copolymer with a poly-ftmctional (usually relatively short) second block that acts as an initiator in the grafting polymerization of the branching monomer even for a step-growth mechanism. In this case the polyfimctionality of the initiator permits control over molecular weights and polydispersity and suppresses homopolymetization. 

Gamier [68]. Recently, poly(jS-pyrrolyl)octanoic acid was synthesized electrochemically in propylene carbonate (Figure 5.29) [73]. Current transient analysis suggested a three-dimensional nucleation and growth mechanism for the film formation on platinum. The polymer films showed high redox stability under repetitive potential cycling. 

Electrochemical homopolymerization of poly(3-thienyl) acetic acid) and copolymers with thiophene were reported to result in polymers consisting of 2000 monomer units. The films were electrochromic in acetonitrile and exhibited optical transitions between golden yellow (reduced) and blue (oxidized) [26]. Electrochemical polymerization was reported to proceed via a two-dimensional layer-by-layer growth mechanism. The rate of propagation of the film was reported to be 0.008-0.14 S cm [27]. No information pertaining to self-doping was reported. 

The ring-opening polymerization of N-carboxyanhydride (NCA) monomers to give poly(peptides) proceeds via a chain-wise or living growth mechanism and has been studied in great detail over the past 15 years. This polymerization has been performed under a variety of conditions, including anionic [87],... 

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