Ts values, while Figure shows the subsequent heating scans. According to the previous definitions of the self-nucleation domains, 183 ºC is a Ts within Domain I, as the sample melted completely, erasing any melt memory in the material and preventing crystallization. If the Ts is lowered to 180 ºC, the sample can be efficiently self-nucleated. This process (i.e., SN) accelerates the non-isothermal crystallization (that comprises both nucleation and growth), and the sample can crystallize with a clear and sharp crystallization exotherm at Tc=127 ºC during cooling from Ts=180 ºC, see Figure . Hence, this temperature is within Domain II. If Ts is further lowered to 176 ºC, the sample enters Domain III, as the temperature falls within the melting range of the material, causing partial melting. The sample is able to crystallize self-seeded by the unmolten crystals (Figure ). The unmolten crystals anneal during the 3 min at Ts=176 ºC and melt in the second heating with a sharp peak at 181 ºC. This is one of the highest melting points reported to date for ROCOP copolymers without tacticity control and furthermore lies far above many recently developed sulfur-containing polymers. Similar melting points for these class of copolymers are have only been achieved where molecular weights are limited (Mn < 20 kg/mol) or not controllable due to e.g. side reactions or zwitterionic propagation pathways. Polarized Light Optical Microscopy (PLOM) reveals that the crystals formed during cooling were smaller than 0.5 m and could not be observed by the limiting resolution imposed by the wavelength of visible light. However, after annealing the samples at room temperature for 2 days, crystal superstructures were able to grow, and their microcrystalline texture of small superstructural aggregates was revealed as seen in Figure . Furthermore, DSC and PLOM were also performed with the sample from Table run #3, which has a similar Mn but less chain regularity (87% ONS-links). Although the sample is also semi-crystalline (Xc = 53% by WAXS), after SN, it crystallizes and melts at lower temperatures than sample #1 (with 95% ONS links). Figure shows the polymer with decreased ONS selectivity forms much smaller crystalline aggregates than the one from Table run #1. Intrigued by the semi-crystallinity of the copolymers we wondered whether this is an inherent feature of these OX copolymers comprising the ONS repeat unit. Copolymerising the saturated analogue of PhNCS namely Cyclohexylisothiocyanate with OX (table 1, run #10) leads to copolymerisation at a reduced rate of 110 h - 1 and polymer selectivity of 89% versus small molecule byproducts. Nevertheless, the copolymer forms in perfect ONS selectivity with a very narrow and monomodal (Đ= 1.08) distribution of Mn = 26.0 kg/mol. The material is amorphous by DSC with a Tg=8 ºC which is also apparent from its' translucent nature. This shows that phenyl substitution is vital for semi-crystallinity which we infer to be due to stacking as the cyclohexyl substituent has similar size but possess no -system for such interactions resulting in an amorphous material. Since our results above show that the copolymerisation methodology tolerates chain transfer reactions with alcohols, we hypothesized that the addition of alcohol-terminated polymers acting as macroinitiators could give easy access to functional block polymers. Hence, we added 20 equivalents of polyethyleneglycol-monomethylether (i.e Me-PEG-OH) to a copolymerisation comprising 1 eq. LCrRb: 1000 eq. OX: 1000 eq. PhNCS and obtained a polymer with a final apparent Mn of 8.0 kDa (Đ = 1.01) after precipitation of the crude mixture from DCM/MeOH. Block polymer formation is clearly indicated by the increase in apparent molecular weight compared to the stand-alone Me-PEG-OH macroinitiator. H NMR spectroscopy of the precipitated polymer in CDCl3 shows an approximate PEG to PhNCS-co-OX repeat unit ratio of 3:1 by integration. Assuming an Me-PEG length of Mn = 5 kDa (as specified by the supplier) and therefore a DP of 133, this corresponds to a DP of the PhNCS-co-OX of approximately 37. Note that some short acetate-initiated chains due to the co-ligands of the LCrRb catalyst might have formed alongside Me-PEG-OH initiated chains via chain-transfer during the polymerisation and might be present in the sample, although the narrow dispersity indicate that the sample primarily composes of diblock polymer. The non-isothermal standard DSC runs (Figure S 38) show that this diblock copolymer features two distinct crystalline phases for the PEG and PhNCS-co-OX blocks respectively with an overall crystallinity by WAXS of Xc = 49%. Once again, Figure shows that SN is an effective way to introduce self-nuclei capable of inducing crystallization upon cooling from the appropriate Ts temperature. Furthermore, as the PhNCS-co-OX block crystallizes at higher temperatures from the self-nucleated melt (between 94 and 142 ºC depending on Ts, see Table ), these crystals can nucleate the PEG block that crystallizes at much lower temperatures (between -21 and 9 ºC).